hello,I am doing project on key management scheme for secure broadcasting.It needs hierarchy of classes similar to e-subscription of newspaper and pay-tv systems.I've done it using three classes like
1.Read,write and download
2. Read and write
3. Read
But the problem is to implement the users subscribing to more than 1 class.and users can join,leave and shift from 1 class to another..can U please suggest me some idea of having different types of classes.

Really your quire is interesting, but you not describe that in which software you built-in your database like sql server , oracle , excel and not mention version also , how can i assume what you what ?